alveoli
gills
AP Biology
Gas Exchange
Respiratory Systems
elephant
seals
2008-2009
AP Biology
Why do we need a
respiratory system?
respiration for
respiration
 Need O2 in
for aerobic cellular respiration
 make ATP

 Need CO2 out

food
waste product from
Krebs cycle
O2
AP Biology
ATP
CO2
Gas exchange
 O2 & CO2 exchange between
environment & cells

need moist membrane

need high surface area
AP Biology
Optimizing gas exchange
 Why high surface area?
maximizing rate of gas exchange
 CO2 & O2 move across cell membrane by
diffusion

 rate of diffusion proportional to surface area
 Why moist membranes?
moisture maintains cell membrane structure
 gases diffuse only dissolved in water

High surface area?
High surface area!
Where have we heard that before?
AP Biology
Gas exchange in many forms…
one-celled
amphibians
echinoderms
insects
fish
mammals
cilia
AP Biology
•
size
water vs. land
•
endotherm vs. ectotherm
Evolution of gas exchange structures
Aquatic organisms
external systems with
lots of surface area
exposed to aquatic
environment
Terrestrial
moist internal
respiratory tissues
with lots of surface area
AP Biology
Gas Exchange in Water: Gills
AP Biology
Counter current exchange system
 Water carrying gas flows in one direction,
blood flows in opposite direction
Why does it work
counter current?
Adaptation!
AP Biology
just keep
swimming….
How counter current exchange works
70%
front
40%
100%
back
15%
water
60%
30%
counter90%
5%
current
blood
50% 70%
100%
50% 30%
concurrent
water
5%
blood
 Blood & water flow in opposite directions

AP Biology
maintains diffusion gradient over whole length
of gill capillary
maximizing O2 transfer from water to blood
Gas Exchange on Land
 Advantages of terrestrial life

air has many advantages over water
 higher concentration of O2
 O2 & CO2 diffuse much faster through air
 respiratory surfaces exposed to air do not have to
be ventilated as thoroughly as gills
 air is much lighter than water & therefore
much easier to pump
 expend less energy moving air in & out
 Disadvantages

keeping large respiratory surface moist
causes high water loss
 reduce water loss by keeping lungs internal
AP Biology
Why don’t
land animals
use gills?
Terrestrial adaptations
Tracheae
 air tubes branching throughout
body
 gas exchanged by diffusion
across moist cells lining
terminal ends, not through open
circulatory system
AP Biology
Lungs
Why is this exchange
with the environment
RISKY?
AP Biology
Exchange tissue:
spongy texture, honeycombed
with moist epithelium
Alveoli
 Gas exchange across thin epithelium of
millions of alveoli

AP Biology
total surface area in humans ~100 m2
Negative pressure breathing
 Breathing due to changing pressures in lungs

air flows from higher pressure to lower pressure

pulling air instead of pushing it
AP Biology
Mechanics of breathing
 Air enters nostrils


filtered by hairs, warmed & humidified
sampled for odors
 Pharynx  glottis  larynx (vocal cords)


AP Biology
mucus traps dust, pollen,
particulates
beating cilia move mucus upward
to pharynx, where it is swallowed
QuickTime™ and a
ompressed) decompressor
eded to see this picture.

 trachea (windpipe)  bronchi 
bronchioles  air sacs (alveoli)
Epithelial lining covered by
cilia & thin film of mucus
don’t want
to have to think
to breathe!
Autonomic breathing control
 Medulla sets rhythm & pons moderates it

coordinate
respiratory,
cardiovascular
systems &
metabolic
demands
 Nerve sensors in
walls of aorta &
carotid arteries in
neck detect
O2 & CO2 in blood
AP Biology
Medulla monitors blood
 Monitors CO2 level of blood

measures pH of blood & cerebrospinal
fluid bathing brain
 CO2 + H2O  H2CO3 (carbonic acid)
 if pH decreases then
increase depth & rate
of breathing & excess
CO2 is eliminated in
exhaled air
AP Biology
Breathing and Homeostasis
 Homeostasis



ATP
keeping the internal environment of the
body balanced
need to balance O2 in and CO2 out
need to balance energy (ATP) production
 Exercise

breathe faster
O2
 need more ATP
 bring in more O2 & remove more CO2
 Disease

poor lung or heart function = breathe faster
 need to work harder to bring in O2 & remove CO2
AP Biology
CO2
Diffusion of gases
 Concentration gradient & pressure
drives movement of gases into & out of
blood at both lungs & body tissue
capillaries in lungs
AP Biology
capillaries in muscle
O2
O2
O2
O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body
Hemoglobin
 Why use a carrier molecule?

O2 not soluble enough in H2O for animal needs
 blood alone could not provide enough O2 to animal cells
 hemocyanin in insects = copper (bluish/greenish)
 hemoglobin in vertebrates = iron (reddish)
 Reversibly binds O2

loading O2 at lungs or gills & unloading at cells
heme group
AP Biology
cooperativity
Cooperativity in Hemoglobin
 Binding O2

binding of O2 to 1st subunit causes shape
change to other subunits
 conformational change

increasing attraction to O2
 Releasing O2

when 1st subunit releases O2,
causes shape change to
other subunits
 conformational change

AP Biology
lowers attraction to O2
O2 dissociation curve for hemoglobin
lowers affinity
of Hb for O2
 active tissue
(producing
CO2) lowers
blood pH
& induces Hb
to release
more O2
AP Biology
% oxyhemoglobin saturation
Bohr Shift
 drop in pH
Effect of pH (CO2 concentration)
100
90
80
70
60
50
40
30
20
10
0
pH 7.60
pH 7.40
pH 7.20
More O2 delivered to tissues
0
20
40
60
80 100
PO2 (mm Hg)
120
140
O2 dissociation curve for hemoglobin
temperature
lowers affinity
of Hb for O2
 active muscle
produces heat
% oxyhemoglobin saturation
Bohr Shift
 increase in
Effect of Temperature
100
90
80
20°C
37°C
70
60
50
40
30
20
10
0
More O2 delivered to tissues
0
AP Biology
43°C
20
40
60
80
PO2 (mm Hg)
100
120
140
Transporting CO2 in blood
 Dissolved in blood plasma as bicarbonate ion
Tissue cells
carbonic acid
CO2 + H2O  H2CO3
CO2
carbonic
anhydrase
bicarbonate
H2CO3  H+ + HCO3–
AP Biology
Carbonic
anhydrase
CO2 dissolves
in plasma
CO2 combines
with Hb
Plasma
CO2 + H2O H2CO3
H2CO3
H+ + HCO3–
Cl–
HCO3–
Releasing CO2 from blood at lungs
 Lower CO2
pressure at lungs
allows CO2 to
diffuse out of
blood into lungs
Lungs: Alveoli
CO2
CO2 dissolved
in plasma
CO2 + H2O
–
+
3 + H
Hemoglobin + COHCO
2
AP Biology
Plasma
HCO3–Cl–
H2CO3
H2CO3
Adaptations for pregnancy
 Mother & fetus exchange
O2 & CO2 across
placental tissue
Why would
mother’s Hb give up
its O2 to baby’s Hb?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
AP Biology
Fetal hemoglobin (HbF)
 HbF has greater attraction to O2 than Hb


low % O2 by time blood reaches placenta
fetal Hb must be able to bind O2 with greater
attraction than maternal Hb
What is the
adaptive
advantage?
AP Biology
2 alpha & 2 gamma units
Don’t be such a baby…
Ask Questions!!
AP Biology
2008-2009